The present invention relates generally to probes for reaction product analyzers such as scanning mass spectrometers and photothermal deflection spectrometers, and more particularly to a sampling probe for delivering reactants to substances such as catalysts and for sampling resulting reaction products.
Various conventional reaction product analyzers are used for analyzing characteristics of reaction products formed by reacting reactants. One such analyzer is a mass spectrometer. One type of spectrometer known as a scanning mass spectrometer may be used to identify the particles present in each reaction product in an array of reaction products. This type of spectrometer has a probe which delivers reactants to each substance (e.g., a catalyst) in an array of substances. The reactants are allowed to react to form reaction products and the probe draws a portion of each reaction product into an ionization chamber of the scanning mass spectrometer for analysis. Using scanning mass spectrometers, hundreds of reaction products can be analyzed over a relatively short period of time. Such scanning mass spectrometers and methods for their use are further described in U.S. Pat. No. 5,959,297, issued Sep. 29, 1999, entitled, “Mass Spectrometers and Methods for Rapid Screening of Libraries of Different Materials”, which is hereby incorporated by reference.
A photothermal deflection spectrometer is another type of reaction product analyzer used to analyze characteristics of reaction products. In photothermal spectrometers, a sample (e.g., a reaction product) is excited with optical radiation from a source such as an infrared laser. The sample absorbs some of the radiation resulting in a change in the sample temperature and density which affect other properties of the sample. Photothermal spectrometers measure the changes in the refractive index of the sample resulting from exciting it with radiation. One such photothermal spectrometer is described in U.S. Pat. No. 6,087,181, issued Jul. 11, 2000, entitled, “Sampling and Detection of Trace Gas Species by Optical Spectrography”, which is hereby incorporated by reference.
Conventional sampling probes used with product analyzers have a recessed tip which is positioned over each substance in an array of substances deposited on a substrate for delivering the reactant and drawing the reaction product. Although the tip does not touch the substrate which holds the substances, it is positioned near the substrate (e.g., within about 100 micrometers) to hold the reactants and reaction products in the recess and to physically prevent them from contaminating adjacent substances in the array. The longer the period of time the reactants are held in the recess, the longer they can react. When a gap is left between the tip and the substrate, the reaction time is generally determined by the diffusion time of the reactants from the center of the recess to its edge. A conventional scanning mass spectrometer probe has a relatively short reaction time, typically on the order of 1 millisecond to about 10 milliseconds.
Due to the inherent limitations of conventional sampling probes, reaction products from low activity reactants are difficult to detect, particularly where relatively long reaction times are required. Further, the conventional sampling probes do not entirely eliminate the potential for contamination of adjacent substances on the substrate.